The first one is to find out the position of the slope potential sliding surface, and the second is to analyze the slope stability in these surfaces. Compute fs against circular arc failure normal method hand solution gnote that slices 1 through 9 have positive. Forces involved for the calculation of stability of slopes. The main objectives of slope stability analysis are finding endangered areas, investigation of potential failure mechanisms, determination of the slope sensitivity to different triggering mechanisms, designing of optimal slopes with regard to safety, reliability and economics, designing possible remedial measures, e.
Slope stability analyses include static and dynamic, analytical or empirical methods to evaluate the stability of earth and rockfill dams, embankments. Dump slope stability evaluation are concerned with. The aim of slope stability analysis of any natural or manmade slope is to determine the failure. The factor of safety and its corresponding critical circular failure surface is required. Such mode of failure greatly differs from the failure on a circular arc which is so far generally assumed in slope stability analysis. The common methods for the analysis of a slope s stability are culmann method, ordinary method of slices and bishop method of slices.
Lines called rays are then drawn from the center of the circle to the centroid point on the circular arc. Most of the methods currently utilized in slope stability analysis are based on the limit equilibrium approach. Mathematical expressions for the circular arc method of. Introduction on circular arc failure of slope analysis.
It is essential that the engineering geologist be intimately familiar with all of these methods because they provide ways of determining, relatively unambiguously, whether a. Methods for analysis of slope stability are described and are illustrated by examples in the appendixes. Critical failure surface, factor of safety, length of failure arc, limit. This program is used to perform slope stability analysis embankments, earth cuts, anchored retaining structures, mse walls, etc. In this study, you get to know some of the methods used and to calculate them. They are certainly major factors in cut slope stability and in. Important aspects in slope stability analysis in this section, three major aspects that influence slope stability analysis are discussed.
Simplicity and relatively good results are the advantages of these methods. This method of slope stability analysis is based on the assumption that the plane of failure is in the form of a circular arc. If the slip surface is an arc of a logarithmic spiral in crosssection, is its shape determined by the angle of. The reference manual for soils and foundations course is intended for. Sliding surface searching method for slopes containing a. The slip surface that has the lowest factor of safety is considered to be the critical failure surface. Most conventional stability analyses of slopes have been made by assuming that the curve of potential sliding is an arc of a circle. The slip circle method of slices is commonly used in the analyses of slope stability and bearing capacity for multilayered ground. Arc stc obtained by random search, the point c is the end point of the weak.
The essential assumption of this approach is the validity of well known mohercoulomb failure criterion which defines the shear strength of. Determination of the critical slip surface in slope stability analysis. The preliminary design process may begin by considering various published stability charts based on simplified assumptions. Methodology of slope stability analysis it is a method to expresses the relationship between resisting forces and driving forces driving forces forces which move earth materials downslope. Pm for normal condition in circular shear surface ss analysis. In 1916, petterson 1955 presented the stability analysis of the stigberg quay in gothenberg. Application and comparison of stability analysis of slope using circular arc method and strength reduction method article pdf available in matec web of conferences 63. Determination of the critical slip surface in slope stability. In the slope failure, the arc of rupture surface meets the slope above the toe. Swedish method of slices example slope stability soil. In this methodthe, mass of soil above the surface of sliding is taken as a unit. Slope stability optimization with noncircular slip surface.
There are several available methods that can be used to perform a circular arc stability analysis for an approach embankment over soft ground. Downslope component of weight of material including vegetation, fill material, or. Intro to slope stability analysis r ced engineering. The methodology is based on the calculation of the safety factor in 2d and 3d using arcgis. Slope stability refers to the condition of inclined soil or rock slopes to withstand or undergo movement. This is possible only when slope angle steep and the soil close to the toe possess high strength. The user interface and analysis options are almost identical to the generalised slope analys is module except for the ability to. Analysis there are three distinct parts to an analysis of the stability of a slope. The slope is said to be stable when its safety factor is greater than one and if its less than one then the slope is said to be unstable. The following document is intended to be a brief overview of the application of slope stability analysis in. Values of f for stability analyses are determined from laboratory tests or estimated from correlations. This method of slope stability analysis is not widely used since it has been found that. Different slope stability analysis software programs were used and compared, and a formula was presented to calculate the length of failure arc by knowing the soil strength parameters.
The slope stability calculated for bishop, janbu, spencer and gle is summarized in the graph below. If x c is determined, the 2d critical slip surface circle center with abscissa x cc must lie on the perpendicular bisector of the straight line from the point of x c to the slope toe o. Slope stability optimization with non circular slip surface and using firefly algorithm, simulate annealing and imperialistic competitive algorithm 82 ajsr civil and enviromental engineering, vol 48, no. This offers a number of methods but, for each analysis, the bishop method was applied for ease of comparison with the fe analysis. In this study, geo5, slope w and flac slope software programs were used to analyze the slope stability problems.
The simplest problem of slope stability that we can analyze, and that we should understand in detail because it is so basic, is that of the stability of the socalled infinite slope. The assumed 2d slope failure surface is circular determined by two variables x c and x cc in figure 2. Practical slip circle method of slices for calculation of. Fs equal to unity is a critical condition where the shear strength of the slope maybe mobilized. Mar 21, 2016 taylors stability number if the slope angle, height of embankment h, the effective unit weight of material, angle of internal friction, and unit cohesion c are known, the factor of safety may be determined. Circular arc failure in embankment fill and foundation soil, c sliding block failure in. Slope stability analysis limit equilibrium or the finite. The rupture surface sets in above the top of the slope fig. In order to simplify the stability analysis process in gis, geometry of more than 100 numbers of existing slope failures were recorded. The geometrical information in 3d for these slope failures were input in the arcgis analytical tool. The geotechnical engineer frequently uses limit equilibrium methods of analysis when studying slope stability problems, for example, ordinary or fellenius method sometimes referred to as the swedish circle method or the conventional method, simplified bishop method, spencers method, janbus simplified method, janbus rigorous method, morgensternprice method, or unified. Theory of slope stability kenneth m cruikshank portland state. The slope geometry and geotechnical parameters are given in fig. Generalised non circular slip analysis slope stability analysis of soil slopes using the nonvertical slice method proposed by sarma non circular slip.
In most limit equilibrium analyses, the minimum shear strength required along a potential failure surface to maintain stability is calculated and then compared to the. Most limit equilibrium methods used in geotechnical. With regard to models used in this study, failure of the slope always initiates at the lower end of the slope, and a approximately triangular zone up to central part of the slope slides. The second is the influence of calculating factor of safety to slope stability and the third aspect is the definition of the slope. The circular sliding surface, as a part of the combined sliding surface, is also ineffective when it intersects with weak structural plane and the node c of weak structural plane falls inside of the circle as shown in fig. Lecture notes, lectures 1012 stability of slopes studocu. The two main objectives of slope stability analysis are calculating fos for a given slip surface and determining the css for a given slope. Pore pressure due to seepage reduces slope stability, but static water pressure, with the same water level inside and outside the slopes, has no effect. The determination of the conditions under which earth slopes will be stable represents one of the most important applications of soil mechanics. Principle of slope stability analysis sliding will occur if the shear stress developed exceeds the corresponding shear resistance of the soil.
The critical slip surface is commonly assumed as a circular arc, logarithmic spiral arc, curve, single plane or multiple planes to simulate the possible sliding movement. Testing of samples to determine the cohesion and angle of internal friction if the analysis is for a natural slope, it is essential that the sample be undisturbed. Application note slope stability analysis worked example. The method of stability analysis used see section 6. It also highlights some of the differences in approach to that adopted by the limit equilibrium method of slices. Results of your manual calculation with the help of excell program. The simplest basic method is known as the normal or ordinary method of slices, also known as fellenius method or the swedish circle method of analysis. Mathematical expressions for the circular arc method of stability analysis richard e. Rock slope engineering civil engineering i am menglim. Determination of slope safety factor with analytical solution and. Application note slope stability analysis worked example 1 introduction this note describes the typical steps followed in setting up and analysing a slope stability problem with limitstate. Slope stability verification manual deep excavation llc page 9. Application of the finite element method to slope stability. X c is the abscissa of a point on slope top surface.
Experience and observations of failures of embankments constructed over relatively deep deposits of soft soils have shown that when failure occurs, the embankment sinks down, the adjacent ground rises and the failure surface follows a circular arc as illustrated in figure below. Use of field, laboratory and theoretical procedures for. Pdf application and comparison of stability analysis of. Fhwa nhi06088 6 slope stability soils and foundations volume i 6 3 december 2006 6. The most important types of slope failure are illustrated in fig. In general, circular slips are associated with homogeneous soil conditions and non circular slips with nonhomogeneous conditions. The swedish circle method, the socalled fellenius slice method, is a widely used. The center of the circle usually lies above the fill slope 33 fill 7 sand 35 clay dense gravel 10 25 2.
The term slope means a portion of the natural slope whose original profile has been modified by artificial interventions relevant with respect to stability. Slope stability causes of instability, analysis methods. Analyzing the stability of earth structures is the oldest type of numerical analysis in geotechnical engineering. The infinite slope solution is also an exact solution, the methods of slices which we examine later are approximate solutions.
Slope stability evaluations by limit equilibrium and. The slope stability analysis is crucial in engineering practice to ensure the stability of structures and prevent loss of human life and money. In this case, failure is assumes at a certain plane w sin. In this method, the potential failure surface is assumed to be a circular arc with centre o and radius r. Chapter 4 slope stability home people at universiti. However, in the case of ground consisting of horizontal sandy layer, it is known that modified fellenius. In rotational slips the shape of the failure surface in section may be a circular arc or a non circular curve. Circular failure analysis most conventional stability analyses of slopes have been made by assuming that the curve of potential sliding is an arc of a circle. Such a study may be adequate in some cases to decide whether a standard slope angle can be used. In this method, the mass of soil above the surface of sliding is taken as a unit. Is the arc of a logarithmic spiral a more critical shape for the crosssectionof the slip surface than a circular arc.
Various techniques of slope stability analysis may be classified into three broad categories. Toe failure occurs when the soil mass of the slope above the base and below the base is mainly homogeneous. Determination of slope safety factor with analytical. The slope stability analysis is generally implemented in two distinct ways. The primary purpose of the slope stability analysis is to contribute to the safe and economic design of mine overburden dump. This was applied in the model by selecting all the boundary lines between the mudstone and weathered mudstone unshow the water table, to facilitate. Determination of slope safety factor with analytical solution. Global stability with relict slip surface in this scenario, the presence of the relict slip surface was assumed. Determination of the critical slip surface in slope. The procedures of stability analysis may be divided into two major categories. Numerical computation of homogeneous slope stability.
It is a practical method for the evaluation of the shortterm stability of saturated clay slopes. Example 1 is taken from the work of griffiths and lane. It was later applied to the problem of slope stability by gilboy. Bvs viswanadham, department of civil engineering, iit.
Slope stability analysis using the limit equilibrium method. Application note slope stability analysis worked example 4. The term landslide refers to a situation of instability affecting natural slopes and involving large volumes of soil. The slip surface is considered as circular bishop, felleniuspetterson, janbu, morgensternprice or spencer methods or polygonal sarma, janbu, morgensternprice or spencer methods.
The stability condition of slopes is a subject of study and research in soil mechanics, geotechnical engineering and engineering geology. Nov 04, 2014 this video is part of the topic slope stability, which cover the different types of slopes, infinite slope analysis, circular slip element analysis, swedish method of slices, bishops method and. The aim of slope stability analysis of any natural or manmade slope is to determine the failure surface that has the lowest factor of safety value. Slope, a limit equilibrium slope stability analysis program, was used. The idea of discretizing a potential sliding mass into slices was introduced early in the 20th century. Limit equilibrium methods are very common method and widely applied to slope stability analysis with various slope shapes and engineering geological conditions ni, 2004, shi and luan, 20. In the lecture part of this course we will discuss a variety of methods of analysis of slope stability and instability. The quantitative determination of the stability of slopes is necessary in a number of engineering activities, such as. The comparative study among the le methods shows that bsm is as good as m.
Taylor 1937 conceived the idea of analyzing the stability of a large number of slopes through a wide range of slope angles and. This engineer manual em provides guidance for analyzing the static stability of slopes of earth and rockfill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock. To guarantee the stability of a homogenous slope, the circular arc method is traditionally used for stability analysis. Instead of assuming a circular failure surface, the slope was analyzed for non circular failure by optimizing surfaces in a path search.
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